Windows Time

I have a windows time server set up on the domain and it has been running for a few months. The problem started on the 19th of April and I have been unable to sync my time. Not sure what happened, but doing a search for the specific error hasn't really turned anything useful up. We are not AD as we still have a NT4 pdc, but my time server is a Windows 2003 server. Does anyone have any idea what could be the root cause? Or have any information at all?
Thank you.